Vehicle wheel alignment apparatus

ABSTRACT

Vehicle wheel alignment apparatus having active alignment determining means operatively mounted on the steerable and non-steerable wheels so as to be substantially insensitive to mechanical distortion of the vehicle wheels and operable in combination with wheel run out compensation means to produce wheel alignment results of improved accuracy, and utilizing the improved arrangement of alignment apparatus for supplying information which can be used for computing the important angular relationship of the wheels to a vehicle reference.

BACKGROUND OF THE INVENTION

The ideal geometric configuration of a four wheel vehicle is a rectanglein which: the steerable wheels will run parallel with each other and areequidistant from the center of the connecting axle or its equivalent; inwhich the non-steerable wheels will run parallel with each other and areequidistant from the center of the connecting axle or its equivalent; inwhich the non-steerable wheels either track with the steerable wheels orare equally off set from the steerable wheel tracks; and in which thevehicle body has its longitudinal geometric center line coincident withthe longitudinal center line for the steerable and non-steerable wheels.

The practical and economic considerations involved in the production ofwheeled vehicles taken into account the complications in connection withmanufacturing tolerances present in the various parts and thepossibility that tolerance mis-matching can build up variations from theideal geometric configuration. As a consequence of the possiblemis-matching of tolerances in the parts making up a finished vehicleprovision is made for mechanically adjusting wheel positions relative tothe chassis or body of a vehicle. In some vehicles all adjustments arefound in the steerable wheel assemblies, while in others the adjustmentsare provided in both the steerable and non-steerable wheel assemblies.Generally vehicles are permitted to have some deviations from the idealconditions of wheel alignment and wheel to body alignment. As along asthe deviations are not regarded as serious the vehicle is put into use.

Wheel alignment apparatus has been disclosed by Manlove U.S. Pat. No.3,181,284 of May 4, 1965 in relation to the steerable and non-steerablewheels of a vehicle. The objective of this disclosure is limited tomechanical apparatus in which mounting members are connected to the rimof the vehicle wheels without being compensated for run out or formechanical variations in the shape of the wheel rims, and in which wheelalignment measurements are made from positions of the measuringapparatus which is displaced from positions representing the truealignment measuring positions. Vehicle wheel alignment apparatus of theelectronic type is disclosed by Florer in U.S. Pat. No. 4,095,902 ofJune 20, 1978, by Lill in U.S. Pat. No. 4,097,157 of June 27, 1978, andby Senften in U.S. Pat. No. 4,126,943 of Nov. 28, 1978.

In connection with the hereinafter to be described wheel compensatingmeans, advantage is taken of the run out compensator method disclosed inSenften U.S. Pat. No. 3,892,042 of July 1, 1975.

BRIEF DESCRPTION OF THE INVENTION

This invention relates to improvements in vehicle wheel alignmentapparatus, and is particularly concerned with the application ofinstrumentation mounted on the steerable and non-steerable wheel sets sothat greatly improved alignment data may be found.

It is a further object of the present invention to dispose the activeinstruments on the various vehicle wheels by mounting means located inthe most advantageous position so as to substantially nullify thephysical inaccuracies in forming the wheel rims and the components ofthe instruments to improve the accuracy of alignment results.

It is an additional object of the present invention to provide, inaddition to compensating the instruments for normal wheel run out,location of the instruments in positions so as to be substantiallyindependent of any deviation of the wheel from the true plane of wheelrotation, whereby mechanical tolerances in wheel as well as ininstrumentation components can be accounted for without substantialinterference in the alignment measuring results.

A preferred embodiment comprises alignment instruments carried by thevehicle wheels in position to be compensated for wheel run out, and tobe operative for measuring alignment angles of the steerable wheels fromthe non-steerable wheel, for measuring the alignment angles of thenon-steerable wheels from the steerable wheels, and for measuring thealignment angles of the steerable wheels from each other in relation toa vehicle reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated in a presently preferred form inthe accompanying drawings, wherein:

FIG. 1 is a side elevational view of steerable and non-steerable wheelsrelated to a typical vehicle shown in silhouette;

FIG. 2 is a diagrammatic plan view of a representative alignment patternfor the wheels of the vehicle seen in FIG. 1;

FIG. 3A is a diagrammatic view of a vehicle wheel and cooperatingalignment instrumentation to illustrate the negligable effect ofmechanical variations in the structure;

FIG. 3B is a side elevation view taken along line 3B--3B in FIG. 3A;

FIG. 4 is a diagrammatic layout of the vehicle wheels for the purpose ofillustrating the measurement of the angles of the respective wheelsrelative to a geometric center line;

FIG. 5 is a fragmentary front view on an enlarged scale of a typicalelectro-optic transducer to illustrate the organization of componentswithout particular regard to the details of the housing;

FIG. 6 is a further view of the transducer components as seen along theline 6--6 in FIG. 5;

FIG. 7 is still another view of the transducer components as seen alongthe line 7--7 in FIG. 5;

FIG. 8 is a block diagram of the electronic circuitry in which onetypical emitter-detector transducer combination has been shown inassociation with signal computation means; and

FIGS. 9A and 9B are diagrams of the transducer components and theireffects on the optical path of the radiant energy beam projected from anemitter.

DETAILED DESCRIPTION OF THE EMBODIMENT

Reference will now be directed to the drawings for a more completeunderstanding of the intent and scope of the invention presented interms of an embodiment presently preferred. The view of FIG. 1 is of apassenger vehicle 14 which will serve to illustrate the utility of thepresently preferred embodiment of the invention. As seen from the leftside, the left steerable wheel 15L is shown in association with one formof an instrument support 16 adapted to grip the flange of the wheel rim.The support 16 carries a pivotal housing 17 the axis of which issubstantially centerable to the spindle axis (not shown) on which thewheel 15L rotates. A bracket 18 is hung from the housing 17 so it mayassume a substantially vertical position even though the wheel 15L isjacked up so it may rotate. At times, with the wheel 15L resting on itssupport, it may be desirable to secure the bracket 18 against pendulusmovement by tightening up on a knob 19 (FIG. 2). The bracket 18, inaddition to the housing 17, carries a support arm 20 which extendsforwardly of the housing 18 to clear the tread of wheel 15L and be inposition so that its end portion may be used for supporting aninstrument device 21L. The support arm 20, or some associated part ofthe assembly, is usually provided with a spirit level (not shown) forpurposes of locating the arm in substantially horizontal position, whichpositioned is retained by tightening up on the knob 19.

FIG. 1 shows the vehicle non-steerable wheel 22L to be provided with aninstrument support 16 which is identical to the support attached to thesteerable wheel 15L. The several parts are designated by similarreference numerals and need not be described again. It is particularlyimportant to observe that the support 16 at the left steerable wheel 15Lcarries an instrument 23L and the support 16 for the left non-steerablewheel 22L carries a companion instrument 24L. These instruments 23L and24L are made up of cooperating components which are intended to functionwith each other in a manner set forth in the contemporaneously filedcopending patent application of James M. Grossman et al, Ser. No.080,274, filed Oct. 1, 1979, and entitled VEHICLE WHEEL ALIGNMENTAPPARATUS.

FIG. 2 shows a schematic plan view of all vehicle wheels, such as thoseat the left side seen in FIG. 1, and companion right side wheels 15R and22R. The wheels at the left side are distinguished by adding the suffix"L", and those at the right side are distinguished by the suffix "R".However, each wheel 15R and 22R is provided with an instrument support16 having the construction generally described above. Also, the support16 on steerable wheel 15R has a support arm 20 which carries aninstrument 21R to cooperate with the left side instrument 21L. Inaddition, the support 16 at the non-steerable wheel 22R carries aninstrument 24R to cooperate with an instrument 23R carried by thesupport 16 at the steerable wheel 15R. These instruments 21L and 21R, aswell as instruments 23R and 24R, cooperate with each other and are madeup of components operating in a manner described in the said Grossman etal patent application.

In view of FIG. 2, the instruments 21L and 23L are operatively connectedinto a console assembly 25 by a lead 26L, and the transducer instruments21R and 23R are similarly connected by a lead 26R to the console 25. Inlike manner the instruments 24L and 24R are connected respectively byleads 27L and 27R into console 25. Signal processing and alignmentcomputation are performed in the console 25 and the results can bedisplayed by means indicated collectively at 28. More particularly inFIG. 2, the instruments 21L and 21R cooperate with each other in theprocess of measuring the angles LWT (left wheel toe) and RWT (rightwheel toe). For that purpose instrument 21L has radiant energy detectormeans which is responsive to a source of radiant energy from instrument21R, and instrument 21R has radiant energy detector means responsive toa source of radiant energy from instrument 21L. The essence of thiscooperation is that projectors of radiant energy are disposed to directbeams in criss-cross paths transversely of the vehicle, and which pathshave boundaries within the field of vision of the detector meansarranged to look at the position from which the beam is projected.

In a like manner, it is indicated in FIG. 2 that instruments 23L and24L, each containing radiant energy beam projectors and radiant energydetectors, cooperate with each other in the process of measuring therespective angles relative to a vehicle reference axis 30 which isestablished by a line joining the center points of the axles 31 and 32,which center points are centered between the spacing of the wheel sets15L and 15R, and 22L and 22R. The angle LFW is formed between the axle31 and the longitudinal line-of-sight L of the radiant energy beam fromthe instrument 24L at wheel 22L. The angle LRW is formed between theaxle 32 and the longitudinal line-of-sight L of the radiant energy beamfrom the instrument 23L at wheel 15L. Similarly, the instruments 23R and24R cooperate with each other for measuring the angles RFW and RRW bythe criss-crossing of the radiant energy beams depicted by the dash lineR representing the longitudinal line-of-sight between the detector meansin the instruments 23R and 24R. In the example seen in FIG. 2, thewheels 15L and 15R have planes of rotation PR which are substantiallyperpendicular to the axle 31, while the planes of rotation PR of thewheels 22L and 22R are also substantially perpendicular to axis 33. Thisarrangement shows that the angles LWT and RWT are substantially ninetydegrees (90°) since it is presumed that the instrument support arms 20are substantially parallel to the planes of rotation PR for wheels 15Land 15R. However, it is shown in FIG. 2 that the tread spacing forwheels 22L and 22R is greater than for the tread spacing of the wheels15L and 15R. In addition, wheel 22L is toed out relative to thereference axis 30 while wheel 22R is toed in relative to the same axis30. The angular positions for the respective wheels 15L, 15R, 22L and22R are arbitrary for purposes of illustrating the unique advantages ofhaving active instruments at each wheel for measuring wheel positionangles from each other and relative to the reference axis 30 for thevehicle.

The Transducers

Turning now to FIGS. 5, 6 and 7, there has been shown in somediagrammatic detail a typical transducer instrument, such as the onedesignated at 21R in FIG. 2. It is to be understood that all of thetransducer instruments 21L, 23L, 24L and 21R, 23R and 24R aresubstantially the same. Thus, the instrument 21R has a panel 34 formedwith an aperture 35 used to control the radiant energy beam. Theaperture 35 may be produced photographically as a transparent area in anopaque material, or the aperture may be an opening in a sheet of solidmaterial. At a suitable distance behind the aperture 35 there aremounted a pair of photodiodes 36 and 37. The width of the aperture 35 issubstantially equal to the width of the face of either one of thesephotodiodes, and it is centered so that, in a null position with radiantenergy impinging at 90° to the plane of panel 34, the exposure of eachphotodiode to the radiant energy should be substantially equal. Thephotodiodes are carried by a printed circuit board PC which also carriespreamplifiers for converting the photodiode output current into voltage,and the operative electronic components associated with radiant energyemitter means 38 which illuminate a cooperative transducer instrumentattached to an adjacent wheel. The photodiodes 36 and 37 are illuminatedby the radiant energy emitter means of that cooperative transducerinstrument.

FIG. 8 is a schematic block diagram of a typical electronic transducerinstrument composed of signal conditioning means 39 connected to anemitter 38. The radiant energy beam generated by the emitter 38 isdirected at detector means in another instrument spaced therefrom wheresuch other instrument has a pair of detectors 36 and 37 located behind awindow 35 in an opaque mask 34. The detectors may be photodiodes havingpreamplifier means 41 and 42 for converting the current generated in thephotodiodes into voltage. These voltage signals are processed inconditioning means 43 to produce output signal A from detector means 41and output signal B from detector means 42, which serves the purpose ofelectronically filtering the detector amplifier signals to isolate theemitter signals and eliminate interference due to noise and ambientlight. The filters are matched to the characteristics of the emittersignals, which may be square wave or sine wave at audio frequency (10KHz for example) so that the detector signals are conditioned bybandpass filters whose center frequency matches the emitter signal. Inorder to obtain angular information the detector signals from thepreamplifiers 41 and 42 and means 43 must be processed in separatecircuits (or in time shared circuit means) in signal computer means 44so as to be able to produce results which can be displayed. When opticalfilter means 45 is employed it is positioned over the aperture 35 and isselected to have transmission characteristics which maximizes all otherlight.

Reference will now be directed to FIGS. 9A and 9B to present a fulldescription of the interaction of the component parts of the tranducer.The boundary of the portion of the radiant energy beam from emitter 38falling through aperture 35 is shown by the dashed lines 38A and 38B.The center of the beam is denoted the line of sight LS. In FIG. 9A theline of sight LS is coincident with the normal axis of the aperture 35.This is the null position in which equal amounts of energy fall ondetectors 36 and 37. In FIG. 9B the detector and aperture assembly, andhence the normal axis NA, is rotated from the line of sight LS. As seenin the drawing, the effect of the aperture 35 is to bound the energybeam such that more light now falls on detector 36 than on detector 37.The electronic current flowing in each detector is proportional to theamount of light incident upon it. The detector signal conditioning means43 of FIG. 8 must measure these currents and convert them to a DCvoltage suitable for signal computation.

A further unique feature of the present embodiment is the way themeasuring instruments are mounted on or supported by the vehicle wheels.The views of FIGS. 3A and 3B will serve to show that mechanical run outpresent in the wheel, as well as tolerances present in the wheel andinstrument, does not materially affect the operation of the instruments21R and 23R. It is assumed in this case that the instrument 23R isprovided with run out compensation means of the type disclosed in SeftenU.S. Pat. No. 3,892,042 (supra) so that the instrument has obtained forits electronic memory the data developed by rotating the wheel 15R froma starting position to a position at 180 degrees of rotation displacedfrom the start, and computing the average of any run out disturbancegenerated in that change of position. For example in FIG. 3A, theinstrument 23R has an ideal position on the axis X--X of wheel rotation.However, the components may have mechanical deviations or physicalirregularities from a perfectly formed system, in which case theinstrument might be located off the axis X--X to the extent of the angleD. Since the irregularities or deviations are local to the wheel 15R,the path along which the instrument may be positioned is the arc C. Thechordal portion of the arc C joining the possible extremes of the angleD is substantially a straight line that essentially coincides with thecompensated plane of rotation of wheel 15R. The mechanical deviation orphysical irregularities which may be present in any vehicle wheel andalso present in an instrument attached thereto include productiontolerances in the components, misshaped wheels, and similar departuresfrom an ideal mechanical assembly. While each instrument 23L, 23R, 24Land 24R embodies the electronic means disclosed in FIG. 5 of SenftenU.S. Pat. No. 3,892,042 to compensate for wheel wobble to find the planeof wheel rotation it also embodies the means of FIG. 8 herein, or it mayembody means of the character seen in Senften U.S. Pat. No. 4,126,943.

In the views of FIGS. 3A and 3B it can be seen that the instrument 21Ris carried on a support 20 which is directly related with the instrument23R. Assuming that the support 20 is related at ninety degrees to theaxis X--X for the wheel 15R, it must follow that the angle D ofdeviation of the instrument 23R, as above outlined, will also be thesame angle D of deviation for instrument 21R. Both instruments 21R and23R are seen to assume positions along a substantially straight line orchord of the arc C and C-1, which positions are dictated by the presenceof mechanical run out in the system. Each instrument embodies radiantenergy emitter means and radiant energy detector means sensitive toreceived radiant energy, but the possible amount of deviation of theline-of-sight is insignificant and can be disregarded.

FIG. 4 is a diagrammatic view of the wheels 15L, 15R, 22L and 22R of thevehicle 14 of FIGS. 1 and 2, but in this view the wheels have beenintentionally misaligned to illustrate the geometry of wheel alignmentinvestigation using the foregoing principle instrumentation. Theinstruments are generally shown and designated by the referencecharacters appearing in FIG. 2, and the alignment is calculated withreference to a geometric center line 30 (FIGS. 2 and 9) of the vehicle.It is necessary to understand that there is a line-of-sight T betweenthe instruments 21L and 21R which represents the radiant energy beampath from the respective instruments 21L and 21R. The line-of-sight maynot be the center of the beam, but the beam has a sufficient spread orfan to be seen by the opposing beam sensors. Normally the wheels willnot be so far out of alignment as is depicted in FIG. 4 that the beamwill not be seen. In like manner there is a line-of-sight L between theinstruments 23L and 24L representing the radiant energy beam path fromthe respective instruments 23L and 24L. The line-of-sight R between theinstruments 23R and 24R depicts the path of the radiant energy beamsfrom those respective instruments. There are construction lines on thedrawing of FIG. 4 to assist in visualing the angles to be investigated,such as the dash lines which are parallel to the geometric center line30, and act as a reference for the angles. It is herein assumed that allmeasured angles have been compensated electronically for wheel run out,as disclosed in the Senften U.S. Pat. No. 3,892,042, to eliminate fromthe following description need to complicate the calculations.

The angles indicated in FIG. 4 are shown in tabular form with referenceto the position of the beam projectors, and beam sensors used todetermine those angles.

    ______________________________________                                        Projector Location                                                                         Sensor Location                                                                              Measured Angle                                    ______________________________________                                        Right front toe arm                                                                        Left front toe arm                                                                           Left cross LC                                     Left front toe arm                                                                         Right front toe arm                                                                          Right cross RC                                    Left rear wheel                                                                            Left front wheel                                                                             Left front                                                                    longitudinal LF                                   Right rear wheel                                                                           Right front wheel                                                                            Right front                                                                   longitudinal RF                                   Left front wheel                                                                           Left rear wheel                                                                              Left rear                                                                     longitudinal LR                                   Right front wheel                                                                          Right rear wheel                                                                             Right rear                                                                    longitudinal RR                                   ______________________________________                                    

The signal information about the angles LC, RC, LF and RF is produced inthe respective instruments (see FIG. 8) and the results are fed into thealignment computer 25 where the following computations relative to thegeometric reference line 30 are worked out for the several anglespertinent to the alignment determination, as follows:

    __________________________________________________________________________    The angles computed                                                                           The computation                                               __________________________________________________________________________    LFT (left front toe)                                                                          1/2(LC + RC + LF - RF)                                        RFT (right front toe)                                                                         1/2(LC + RC - LF + RF)                                        TFT (total front toe)                                                                         LFT + RFT = LC + RC                                           SB (set back)   1/2(RC - LC + LF - RF)                                        LRT (left rear toe)                                                                           LFT - LF + LR = (LC + RC - LF - RF) + LR                      RRT (right rear toe)                                                                          RFT - RF + RR = 1/2(LC + RC - LF - RF) + RR                   TRT (total rear toe)                                                                          LRT + RRT = LC + RC - LF - RF + LR + RR                       TL (thrust line)                                                                              1/2(LRT - RRT) = 1/2(LR - RR)                                 LFTTH (left front toe                                                                         LFT - TL                                                      relative to thrust line)                                                      RFTTH (right front toe relative                                                               RFT + TL                                                      to thrust line)                                                               __________________________________________________________________________

After the computation has been made it is in a form suitable for drivingthe display 28. The display may be a group of meters (not shown) forshowing the values of the computed angles identified in the left columnabove. It is usual in the make up of display 29 to provide meters andcircuit selectors for connecting the meters selectively to display left,right and total toe for the steerable wheels, or left, right and totaltoe for the non-steerable wheels, or wheel set back, or the relationshipof steerable wheel toe relative to the thrust line for the non-steerablewheels.

In view of the foregoing disclosure it is apparent that the presentapparatus has certain unique characteristics which are adapted toproduce more accurate vehicle wheel alignment information by means whichenables an alignment service shop to determine quickly and easily therespective angular relationships of the individual wheels of a vehiclewith respect to a vehicle reference line. A unique feature resides inthe way that the instruments are mounted on the respective wheels sothat signals representative of the individual wheel positions aregenerated directly and can be fed into a remote computer console forcomputation and display. In the mounting of the instruments at each ofthe vehicle wheels a support is selected for the instrument to place itin a position such that the instrument will be substantially independentof any mechanical irregularities of the character above defined. Thislatter feature is disclosed in FIGS. 3A and 3B where it has beendisclosed that mechanical irregularities might result in positioning theinstrument 23R at any place along the path of arc C, and regardless ofthe precise position along this arc, the emitter and detector means willnot be displaced to any significant degree since there is extremelyslight shifting of the poisition away from the arcuate path C. In likemanner, with respect to the instrument carried by the front support arm,instrument 21R on the support 20 would be insignificantly displacedsince the emitter and sensor would be moving in the arcuate path C-1which has only slight lateral displacement of an amount that can beignored.

The present disclosure has set forth a unique arrangement for vehiclewheel alignment apparatus which will produce greatly improved accuracyin determining the position of the respective vehicle wheels relative toa vehicle reference line, which in connection with the view of FIG. 2has been indicated to be the geometric center line of the vehicle. Whilethe foregoing disclosure has set forth a preferred embodiment of thepresent invention it should be understood that variations therefrom maycome to mind after the principals of the disclosure have beenunderstood, and it is desired to include all reasonable variationswithin the scope of this disclosure.

What is claimed is:
 1. In apparatus for determining the alignmentpositions of vehicle wheels in relation to a reference axis of thevehicle and to the thrust line of the non-steerable wheels, theimprovement which comprises:(a) first alignment determining instrumentscarried by each of a set of steerable wheels so as to be in asubstantially vertical plane containing the axis of rotation of saidsteerable wheels; (b) second alignment determining instruments carriedby each of a set of non-steerable wheels so as to be in a substantiallyvertical plane containing the axis of rotation of said non-steerablewheels; (c) third alignment determining instruments supported from saidsteerable wheels in position to be in line-of-sight with each othertransversely of the vehicle; (d) radiant energy beam projectors and beamsensors in each of said first, second and third alignment determininginstruments in positions such that the radiant energy beams from firstinstruments are in the line-of-sight to be sensed by said beam sensorsin second instruments, radiant energy beams from second instruments arein the line-of-sight to be sensed by said beam sensors in firstinstruments, said first and second instruments are arranged incooperating pairs along opposite longitudinal sides of the vehicle so asto be spaced in the longitudinal direction between said steerable andnon-steerable wheels; and (e) radiant energy beam projectors and beamsensors in said third alignment determining instruments in positions ofcooperation transversely of the vehicle adjacent the steerable wheels,whereby said first and third instruments cooperate to generate signalsdeterminative of the alignment positions of the steerable wheelsrelative to the vehicle reference axis and said second instrumentscooperate with said first instruments to generate signals determinativeof the thrust line effect of the non-steerable wheel on said steerablewheels.
 2. Apparatus for determining the angular relationship of thesteerable and non-steerable wheels of a vehicle relative to alongitudinal reference axis of the vehicle and the thrust line of thenon-steerable wheels, the apparatus being associated with the wheels insets longitudinally spaced a distance representing the vehicle wheelbase and the wheel tread width, said apparatus comprising:(1) first andsecond wheel position determining instruments carried by each wheel ofthe steerable wheel set;(a) a first one of said instruments being inline-of-sight with each other transversely of the vehicle; (2) a singleangle determining instrument carried by each non-steerable wheel inposition to be in line-of-sight with a second instrument carried by asteerable wheel at the same longitudinal side of the vehicle, (a) saidsingle instruments and said second instruments being located insubstantial alignment with the axis of rotation of the vehicle wheels onwhich each is carried, such that each instrument represents the plane ofwheel rotation; (3) and all of said instruments being cooperativelyoperable for generating signals representative of the positions of theindividual wheels in said sets for determining the thrust line positionsof the non-steerable wheels relative to the longitudinal reference axisof the vehicle, and for determining the effect on the positions of thesteerable wheels of the thrust line alignment of the non-steerablewheels.
 3. Apparatus for determining the angular alignment relationshipof the steerable and non-steerable wheels of a vehicle relative to alongitudinal reference axis of the vehicle to the thrust line of thenon-steerable wheels, the apparatus being associated with thearrangement of the longitudinally and transversely spaced wheelsrepresenting the vehicle wheel base and tread width dimensions, saidapparatus comprising:(1) a pair of alignment determining instrumentsmounted on each of the steerable wheels,(a) with a first one of saidinstruments on each steerable wheel being positioned to alignsubstantially with the axis of wheel rotation so as to have a minimum oflateral displacement to the vehicle longitudinal reference axis uponturning of the steerable wheels, (b) and a second one of saidinstruments on each steerable wheel being positioned forwardly of thewheels so that said second instruments are in position for obtainingcooperation therebetween transversely of the vehicle wheels; (2) asingle measuring instrument on each of the non-steerable wheels inposition to align substantially with the axis of wheel rotation, suchthat each instrument represents the plane of wheel rotation, (3) saidfirst ones of said instruments being positioned to be in alignmentdetermining cooperative relationship with said single instrumentspositioned at the same side of the vehicle wheel base, and said secondones of the instruments being in alignment determining cooperativerelationship with each other across the tread width of the vehicle,(a)said instruments generating signals representive of the position of therespective wheels relative to the vehicle reference axis and the thrustline of the non-steerable wheels; (4) and alignment computer meansoperatively connected with each of said instruments and including meansto display the values of the computed angles from the signals generatedby said instruments,(a) such that the toe alignment determination of thesteerable wheels and the non-steerable wheels and the thrust linealignment determination of the non-steerable wheels is displayed inrelation to the vehicle longitudinal reference axis.
 4. Apparatus fordetermining the existing alignment of the steerable and non-steerablevehicle wheels relative to a longitudinal reference axis of the vehicleand to the thrust line of the non-steerable wheels, in which theapparatus comprises:(1) six alignment determing instruments, eachembodying a radiant energy projector and signal generating radiantenergy sensor means mounted such that(a) each non-steerable vehiclewheel supports one instrument in position to represent the plane ofrotation of that wheel and in alignment with its axis of rotation, (b)each steerable vehicle wheel supports a first instrument in position torepresent the plane of rotation of that wheel and in alignment with itsaxis of rotation, and (c) each steerable vehicle wheel also supports asecond instrument in position to represent the angular position of theplane of rotation of that wheel relative to the longitudinal referenceaxis of the vehicle; (2) said one instrument at each non-steerable wheelbeing in line-of-sight with said first instrument at each steerablewheel at the same longitudinal side of the vehicle for mutualcooperation therewith, such that(a) the radiant energy sensors in saidone instrument and said first instrument are energized by the radiantenergy projected from the projectors in said first instrument and saidone instrument respectively; (3) said second instruments being in mutualcooperative line-of-sight positions such that(a) the radiant energysensor in each instrument is energized by the radiant energy projectedfrom the projector in the cooperative instrument; (4) said signalsgenerated by said sensors representing the position of the respectivevehicle wheels; (5) and means operatively connected to each individualinstrument for processing the signals generated by each of said radiantenergy sensors such that(a) the toe alignment of the steerable wheelsand the toe alignment and thrust line of the non-steerable wheels isdetermined in relation to the longitudinal reference axis of thevehicle. .Iadd.
 5. A wheel alignment measuring apparatus designed formeasuring wheel alignment angles of the vehicle having front and rearwheels and comprising:six angle measuring units, first and second saidangle measuring units adapted for connection respectively to the leftand right front wheels of the vehicle and including angle pickup meansfor measuring and producing signals indicating the total tracking anglesof both front wheels, third and fifth said angle measuring units adaptedfor connection respectively to the left front wheel and a left rearwheel and including angle pickup means for measuring and producingsignals indicating the angles of these wheels, and fourth and sixth saidangle measuring units adapted for connection respectively to the rightfront wheel and a right rear wheel and including angle pickup means formeasuring and producing signals indicating the angles of these wheels,means rigidly joining the first said angle measuring unit with saidthird angle measuring unit, means rigidly joining said second anglemeasuring unit with said fourth angle measuring unit, and an electricalcircuit means for receiving signals from said angle pickup means and forproducing a reading for wheel alignment data from the angles measured bysaid angle measuring units. .Iaddend. .Iadd.
 6. The structure as claimedin claim 5 wherein said angle measuring units have relative placementsand polarities arranged to cut out effects produced by track differencesand wheel base differences so that output readings are produced free ofsuch differences. .Iaddend.